changing the home directory of usermain to /home is not going to do anything as the setting is just a way to help users find there home folders, not perform permissions.
So basically you will have to do it with permissions, now this type of functionality is done by the group setting, so first you change the permissions of user folders to be 771, then you give each user there own group, if they already dont have there own group and then add the name of each users group to usermain group.
now this will give you read access to all the users, but not right access, YET.
now on unix we have stupidness, this is in the form of primary group and other groups.
So basically you can belong to any number of groups BUT only one master group.
And to edit one of the users folders you need there group name as your master group.
And changing the master group is done with a command which i have forgotten, someone look it up and report it.
Ow and you cannot add everyone to the same group as they would have access to each others home directory, just incase you think of doing this.